With an initial temperature difference of 50 degrees between the coffee and the room, the coffee cooled 25 degrees in 8 hours. Newton’s law of cooling says that the rate of cooling is proportional to the temperature difference. Now the initial temperature difference is half as great as in the first case. Because the rate of cooling is half as great, we expect that in 8 hours, the coffee will cool half as much as it did in the first eight hours. It will cool by another 12.5 degrees.